According to the speaker in a talk I went to several years ago, it was the case until some time last century that educated Chinese people would have memorized hundreds of books going back as far as thousands of years. And these books wove together in a thicket of references: when an author wrote a phrase, it wouldn’t just be an allusion to a phrase/incident in a single book X. Instead, it would be an allusion to a phrase in book A written two thousand years ago and also to phrases is books B, C, D, and E that were written over the intervening centuries/millennia that all also alluded back to book A.